\documentclass{scrartcl}
\usepackage{xintgcd,xintfrac}

\newcommand*\reducedfrac[2]
{\begingroup
	\edef\gcd{\xintGCD{#1}{#2}}%
	\frac{\xintNum{\xintDiv{#1}{\gcd}}}{\xintNum{\xintDiv{#2}{\gcd}}}%
	\endgroup}

\begin{document}
\[
	\frac{278922}{74088} = \reducedfrac{278922}{74088}
\]
\end{document}
